Novel block copolymers containing benzocyclobutene units

ABSTRACT

Novel, reactive block copolymers are claimed having the structures AB, ABA, (AB) m  Y, (AB) n  Y--A) o  and (AB) n  Y--B) p  where each A block is a copolymer block of a monoalkenyl arene monomer and a benzocyclobutene monomer of the formula ##STR1## where R is H or CH 3  and each B block is a polymerized conjugated diene hydrocarbon block.

FIELD OF THE INVENTION

The present invention is directed to novel block copolymers ofmonoalkenyl arenes and/or conjugated dienes. More particularly, thepresent invention is related to novel block copolymers of monoalkenylarenes, conjugated dienes and derivatives of benzocyclobutene, whichpolymers may be crosslinked at elevated temperatures.

BACKGROUND OF THE INVENTION

Block copolymers have been developed rapidly within the recent past, thestarting monomers usually being monoalkenyl arenes such as styrene oralphamethyl styrene block polymerized with conjugated dienes such asbutadiene and isoprene. A typical block copolymer of this type isrepresented by the structure polystyrene-polybutadiene-polystyrene. Whenthe monoalkenyl arene blocks comprise less than about 55% by weight ofthe block copolymer, the product is essentially elastomeric. Moreover,due to their peculiar set of physical properties they can be referred tomore properly as thermoplastic elastomers. By this is meant polymerswhich in the melt state are processable in ordinary thermoplasticprocessing equipment but in the solid state behave like chemicallyvulcanized rubber without chemical vulcanization having been effected.Polymers of this type are highly useful in that the vulcanization stepis eliminated and, contrary to scrap from vulcanized rubbers, the scrapfrom the processing of thermoplastic elastomers can be recycled forfurther use.

These block copolymer have enjoyed broad commercial success.Nevertheless, improvements in such polymers are desired. In particular,for particular applications such polymers require greater solventresistance and higher use temperatures. Still further, such polymersalso need improved adhesion to polar materials when used in certainblend compositions. What has now been discovered is a new blockcopolymer that overcomes these deficiencies.

SUMMARY OF THE INVENTION

The present invention relates broadly to novel copolymers of monoalkenylarenes and/or conjugated dienes with a benzocyclobutene derivative. Inparticular, the present invention relates to a block copolymer selectedfrom the group consisting of AB block copolymers, ABA block copolymers,(AB)_(m) Y block copolymers, (AB)_(n) Y--A)_(o) block copolymers,(AB)_(n) Y--B)_(p) block copolymers and mixtures thereof where each "A"is a copolymer block of a monoalkenyl arene monomer and abenzocyclobutene monomer of the formula ##STR2## where R is H or CH₃,each "B" is a polymerized conjugated diene hydrocarbon block, "m", "n","o" and "p" are each 1 to about 30 and Y is the residue of amultifunctional coupling agent or multifunctional initiator.

The invention also relates to a process for preparing such polymers.

ADVANTAGES OF THE INVENTION

The polymers of the present invention possess a number of advantagesover prior art block copolymers. When the polymers of the presentinvention are crosslinked at elevated temperatures, the resultingpolymers possess improved solvent resistance along with higher usetemperatures. In addition, it is possible to functionalize suchnon-crosslinked polymers to obtain polymers having improved adhesion topolar materials.

DETAILED DESCRIPTION OF THE INVENTION

The block copolymers of the present invention have idealized structuresas follows:

    ______________________________________                                        Structure     Type                                                            ______________________________________                                        AB            2 block copolymer                                               ABA           linear block copolymer                                          (AB) .sub.mY  radial block copolymer                                          (AB) .sub.nY(A).sub.o                                                                       assymetric radial block copolymer                               (AB .sub.nY(B).sub.p                                                                        assymetric radial block copolymer                               ______________________________________                                    

Mixtures of the above structures are also contemplated.

The "A" blocks are copolymer blocks of a monoalkenyl arene monomer and abenzocyclobutene monomer of the formula ##STR3## where R is H or CH₃.When R is H, the benzocyclobutene monomers are 4-vinylbenzocyclobuteneor 3-vinylbenzocyclobutene. When R is CH₃, the benzocyclobutene monomersare 4-isopropenylbenzocyclobutene or 3-isopropenylbenzocyclobutene. Thepreferred benzocyclobutene monomer is 4-vinylbenzocyclobutene.Preferably the monoalkenyl arene is styrene. Other useful monoalkenylarenes include alphamethyl styrene, tertbutyl styrene, paramethylstyrene and the other ring alkylated styrenes as well as mixtures of thesame.

The relative amounts of benzocyclobutene monomer and monoalkenyl arenemonomer in the A blocks depends upon the desired functionality or degreeof crosslinks. The table below shows suitable ranges in mole percent:

    ______________________________________                                                        Preferred                                                                             More Preferred                                        ______________________________________                                        Benzocyclobutene monomer                                                                         0.01 to 20                                                                              0.1 to 10                                        Monoalkenyl arene monomer                                                                       99.99 to 80                                                                             99.9 to 90                                        TOTAL             100       100                                               ______________________________________                                    

The B blocks are polymer blocks of conjugated dienes. Preferred dienesinclude butadiene and isoprene. A much preferred diene is butadiene.Mixtures of conjugated dienes may also be employed.

The Y moiety stands for the residue of a multifunctional coupling agent.Linear polymers (ABA) are formed by employing coupling agents having tworeactive sites or by sequential polymerization. One type of couplingagent employed in the forming linear polymers is a dihalo alkane such asdibromoethane. See G.B. Pat. No. 1,014,999. Another coupling agentemployed in making linear polymers is phenyl benzoate as disclosed inU.S. Pat. No. 3,766,301. Radial polymers are formed by employingcoupling agents having more than two reactive sites. Examples of suchcoupling agents include among others: SiCl₄ --U.S. Pat. No. 3,244,664;Polyepoxides, polyisocyanates, polyimines, polyaldehydes, polyketones,polyanhydrides, polyesters, polyhalides--U.S. Pat. No. 3,281,383;Diesters--U.S. Pat. No. 3,594,452; Methoxy silanes--U.S. Pat. No.3,880,954; Divinyl benzene--U.S. Pat. No. 3,985,830;1,3,5-benzenetricarboxylic acid trichloride--U.S. Pat. No. 4,104,332;and glycidoxy-methoxy silanes--U.S. Pat. No. 4,185,042.

The linear and radial block polymers may also be formed by sequentialpolymerization using multi-functional initiators having ≧2 reactivecarbon-lithium bonds. The dilithium initiators are represented by theformula LiRLi. Examples of these dilithium initiators are1,1,6,6-tetraphenyl-1,5-hexadiene, 1,3-divinylbenzene,1,3-bis(1-methylvinyl)benzene, 1,4-bis(2-phenylvinyl)benzene,1,3-bis(1-phenylvinyl)benzene, 1,4-bis(1-phenylvinyl)benzene,4,4'-bis(1-phenylvinyl)biphenyl, 2,7-diphenyl-1,7-octadiene,2,7-di-4-tolyl-1,7-octadiene, 1,2-bis(4-(1-phenylvinyl)phenyl)-ethane,and 1,4-bis(4-(1-phenylvinyl)phenyl)butane. Initiators with more thantwo lithium-carbon bonds can be formed by the reaction of RLi and DVB.

The letters "m", "n", "o" and "p" stand for the relative number of armsin each polymer molecule. Accordingly, m, n, o and p are integers whenreferring to a single polymer molecule. However, a polymer mass willgenerally contain molecules of varying functionality. When referring tothe polymer (AB)_(m) Y, it is preferred that m be 1 to 15, preferable 2to 8. When referring to the polymers (AB)_(n) Y--A)_(o) and (AB)_(n)Y--A)_(p), it is preferred that the sum of n+o be greater than 3,preferably 3 to 15 and that the sum of n+p be greater than 3, preferably3 to 15. Accordingly n is preferably 2 to 8 for both polymers.

The polymers of the present invention are produced by anionicpolymerization employing an organomonolithium initiator. (The followingdescription refers only to mono-lithium initiators, though it isappreciated, as stated above, that multi-functional initiators may alsobe used.) The first step of the process involves contacting themonoalkenyl arene monomer benzocyclobutene monomer and theorganomonolithium compound (initiator) in the presence of an inertdiluent therein forming a living polymer compound having the simplifiedstructure A-Li. The monoalkenyl arene is preferably styrene. The inertdiluent may be an aromatic or naphthenic hydrocarbon, e.g., benzene orcyclohexane, which may be modified by the presence of an alkene oralkane such as pentenes or pentanes. Specific examples of suitablediluents include n-pentane, n-hexane, isooctane, cyclohexane, toluene,benzene, xylene and the like. The organomonolithium compounds(initiators) that are reacted with the polymerizable additive in stepone of this invention are represented by the formula R¹ Li; wherein R¹is an aliphatic, cycloaliphatic, or aromatic radical, or combinationsthereof, preferably containing from 2 to 20 carbon atoms per molecule.Exemplary of these organomonolithium compounds are ethyllithium,n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium,tertoctyllithium, n-decyllithium, n-eicosyllithium, phenyllithium,2-naphthyllithium, 4-butylphenyllithium, 4-tolyllithium,4-phenylbutyllithium, cyclohexyllithium,3,5-di-n-heptylcyclohexyllithium, 4-cyclopentylbutyllithium, and thelike. The alkyllithium compounds are preferred for employment accordingto this invention, especially those wherein the alkyl group containsfrom 3 to 10 carbon atoms. A much preferred initiator issec-butyllithium. See U.S. Pat. No. 3,231,635. The concentration of theinitiator can be regulated to control molecular weight. Generally, theinitiator concentration is in the range of about 0.25 to 50 millimolesper 100 grams of monomer although both higher and lower initiator levelscan be used if desired. The required initiator level frequently dependsupon the solubility of the initiator in the hydrocarbon diluent. Thesepolymerization reactions are usually carried out at a temperature in therange of -75° to +150° C. and at pressures which are sufficient tomaintain the reaction mixture in the liquid phase.

Next, the living polymer in solution is contacted with a conjugateddiene. Preferred dienes include butadiene and isoprene. A much preferreddiene is butadiene. The resulting living polymer has a simplfiedstructure A--B--Li. The predominantly cis-1,4 microstructure of thepolybutadiene blocks obtained from polymerization in cyclohexane can bemodified to a random mixture of 1,4- and 1,2-structures by the additionof a small amount of ether modifiers such as Et₂ O, THF, etc.

The B-Li polymer arms may be formed in a separate reactor employing aninert solvent, organomonolithium initiator and conjugated diene monomer.In an alternative embodiment, the B-Li arms may be formed in the samereactor as the AB-Li polymer arms. In that case, after the A-Li arms areformed, additional initiator is added. Then the conjugated diene monomeris added. In this alternative embodiment, the B arms and the B portionof the AB arms will necessarily be similar in composition and molecularweight.

The molecular weights of the living polymer arms (A and B) may varybetween wide limits. Suitable number average molecular weights are:

    ______________________________________                                                Preferred  More Preferred                                             ______________________________________                                        A           300 to 30,000                                                                             3,000 to 20,000                                       B         15,000 to 100,000                                                                          25,000 to 60,000                                       ______________________________________                                    

The living AB-Li and B-Li or A-Li polymer arms are then reacted with amultifunctional coupling agent. Exemplary coupling agents are listedabove. The AB and ABA polymers do not require use of coupling agents.

The coupling agent should be aded to the living polymer after thepolymerization of the monomers is substantially complete, i.e., theagent should only be added after substantially all of the monomer hasbeen converted to living polymers.

The amount of coupling agent added depends upon the structure of thecoupling agent and on the desired number of arms, and the choice iswithin the skill of the average polymers chemist.

The coupling reaction step may be carried out in the same solvent as forthe polymerization reaction step. A list of suitable solvents is givenabove. The coupling reaction step temperature may also vary between widelimits, e.g., from 0° to 150° C., preferably from 20° to 120° C. Thereaction may also take place in an inert atmosphere, e.g., nitrogen andunder pressure e.g., a pressure of from 0.5 to 10 bars.

Following the coupling reaction, the polymer product may be hydrogenatedaccording to copending application Ser. No. 812,424, now U.S. Pat. No.4,687,815, or functionalized.

Then the product is typically recovered such as by coagulation utilizinghot water or steam or both.

A key aspect of the present invention is that the end product containsrandomly distributed benzocyclobutene structures in the styrene endblocks. A schematic structure for an ABA block copolymer is shown below,where the monoalkenyl arene block is made from styrene (S) and the dieneblock is made from butadiene (B): ##STR4##

Accordingly, when such a polymer is molded at temperatures above about200° C. (or otherwise heated above such temperatures), a crosslinkedelastomer is obtained.

To illustrate the instant invention, the following illustrativeembodiments are given. It is to be understood, that the embodiments aregiven for the purpose of illustration only and the invention is not tobe regarded as limited to any of the specific materials or conditionsused in the specific embodiments.

ILLUSTRATIVE EMBODIMENTS I

A key aspect of the present invention deals with the ring-opening of thebenzocyclobutene monomers to reactive o-quinodimethanes. In thisembodiment, half-life values for the parent benzocyclobutene arecalculated and summarized in the following Table 1, based on activationparameters reported in W. R. Roth et al Chem. Ber. 111, 3892-3903(1978). The results suggest that reactive oligomers and polymerscontaining benzocyclobutenes which are not substituted at thecyclobutene ring would have long shelf-life and good reactivity at200°-250° C.

                  TABLE 1                                                         ______________________________________                                         ##STR5##                                                                     T (°C.)                                                                              k (sec.sup.-1)                                                                              t.sub.1/2 (hr)                                    ______________________________________                                         25           2.5 × 10.sup.15                                                                       7.6 × 10.sup.10                             100           1.7 × 10.sup.-9                                                                       1.1 × 10.sup.5                              150           9.6 × 10.sup.-7                                                                         2 × 10.sup.2                              200           1.4 × 10.sup.-4                                                                       1.4                                               250           7.8 × 10.sup.-3                                                                       2.5 × 10.sup.-2                             ______________________________________                                    

ILLUSTRATIVE EMBODIMENT II Preparation of 4-vinylbenzocyclobutene

A solution of 4-chloromethylbenzocyclobutene (24.4 g, 160 mmol) andtriphenylphosphine (41.9 g, 160 mmol) in 120 ml of chloroform was heatedat reflux for 24 h. Addition of diethyl ether followed by filtrationgave tripheny(4-benzocyclobutenyl)methyl phosphonium chloride as a whitepowder: ¹ H NMR (CDCl₃) δ3.03 (m, 4H), 5.36 (d, 2H), 6.82 (m, 3H),7.6-7.8 (m, 15H). To a solution of the phosphonium salt in 500 ml of 37%formaldehyde in water was added dropwise 75 ml of 50% aqueous sodiumhydroxide. The mixture was stirred at ambient temperature for 2 h andthen extracted with diethyl ether. The ether extract was washed withbrine and dried over magnesium sulfate. Fractional distillation gave14.5 g of 90% pure 4-vinylbenzocyclobutene: bp 63°-66° C. (6 torr); ¹ HNMR (CDCl₃) δ3.11 (s, 4 H), 5.11 (d, 1H), 5.63 (d, 1H), 6.66 (dd, 1H),6.95 (d, 1H), 7.10 (s, 1H), 7.18 (d, 1H); ¹³ C NMR (CDCl₃) δ29.29,29.44, 112.27, 119.87, 122.52, 125.70, 136.72, 137.97, 146.66, 146.01.##STR6##

ILLUSTRATIVE EMBODIMENT III Preparation of Styrene-Butadiene TriblockPolymers with 4-vinylbenzocyclobutene in the Styrene Block

To a solution of styrene (9.73 g, 93.6 mmol), 4-vinylbenzocyclobutene164 mg, 1.26 mmol), and 25 μl of 1-η-butoxy-2-t-butoxyethane in 233 g ofcyclohexane was added 1.3 mmol of s-butyl lithium. After the mixture washeated at 50° C. for 30 min under an inert atmosphere, butadiene (25.6g, 474 mmol) was added and the heating was continued for an additional2.5 h. The polymerization was terminated by the addition of 0.5 mmol ofmethyl benzoate. GPC analysis showed the product to be a mixture ofpolystyrene (7.9% MW 7,500), styrene-butadiene diblock (35.4%, MW28,000), styrene-butadiene-styrene triblock (54.4%, MW 58,000), andstyrene-butadiene multiblock (2.3%, 106,000). ¹ H NMR showed the productto contain 28%W styrene, 1.2%m 4-vinylbenzocyclobutene in the styreneblock, and 40%m vinyl in the butadiene block.

ILLUSTRATIVE EMBODIMENT IV

Various styrene-butadiene-styrene block copolymers with4-vinylbenzocyclobutene (VBC) in the styrene blocks were prepared in amanner similar to that used in Illustrative Embodiment III.

Reactive styrene-butadiene-styrene block polymers containing VBC wereprepared using styrene monomer containing 1.3%m of VBC. Thepolymerizations were carried out in glass bottles at 50° C. incyclohexane using s-BuLi as initiator and the results are summarized inTable 1. Styrene-butadiene-styrene triblock polymers were prepared bysequential anionic polymerization of styrene and butadiene using twicethe theoretical amounts of BuLi followed by coupling the living diblockpolymers with methyl benzoate. GPC analysis showed the products to bemixtures of diblock and triblock polymer whose experimental molecularweights were in good agreement with those calculated based on zeroconsumption of BuLi by impurities. The coupling efficiencies based ofmethyl benzoate were generally in the range of 70-80% (Table 2).

The presence of benzocyclobutene in the products can be readilyconfirmed by the magnetic resonance of the ethylene protons inbenzocyclobutene at δ3.1 ppm. Quantitative ¹ H NMR showed thestyrene-butadiene-styrene triblock polymer to contain 1.2%m VBC based onstyrene. This value agrees well with that of 1.3%m VBC in styrenemonomer.

                  TABLE 1                                                         ______________________________________                                        Comparison of Calculated and GPC Molecular Weights                             ##STR7##                                                                                  SBBS MW (× 10.sup.3)                                       17317-28-#   Calculated    Found                                              ______________________________________                                        1            5.1-25.2-5.1  4.5-23.4-4.5                                       2            5.1-26.8-5.1  4.6-25.5-4.6                                       3            7.6-37.8-7.6  7.1-40.7-7.1                                       4            7.6-39.4-7.6  7.5-43.1-7.5                                       5            5.0-25.4-5.0  4.5-24.8-4.5                                       6            7.6-40.0-7.6  7.3-44.4-7.3                                       ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                % SBBS                                                                17317-28-#                                                                              Calculated  Found   Coupling Eff. (%)                               ______________________________________                                        1         78          58      73.4                                            2         79          50      63.3                                            3         77          62      80.5                                            4         77          54      70.1                                            5         79          61      77.2                                            6         77          62      80.5                                            ______________________________________                                    

What is claimed is:
 1. A block copolymer selected from the groupconsisting of AB block copolymers, ABA block copolymers (AB)_(m) Y blockcopolymers, (AB)_(n) Y--A)_(o) block copolymers, (AB_(n) Y--B)_(p) blockcopolymers and mixtures thereof where each "A" is a copolymer block of amonoalkenylarene monomer and a benzocyclobutene monomer of the formula##STR8## where R is H or CH₃, each "B" is a polymerized conjugated dienehydrocarbon block, "m", "n", "o" and "p" are each 1 to about 30 and Y isthe residue of a multifunctional coupling agent or multifunctionalinitiator.
 2. The block copolymer of claim 1 where said monoalkenylarene monomer is styrene and said conjugated diene is selected from thegroup consisting of butadiene and isoprene.
 3. The block copolymer ofclaim 1 wherein said benzocyclobutene monomer is4-vinylbenzocyclobutene.
 4. The block copolymer of claim 2 wherein thenumber average molecular weight of the A block(s) are 300 to 30,000 andthe number average molecular weight of the B block(s) are 15,000 to100,000.
 5. The block copolymer of claim 1 wherein the A block comprisesabout 0.01 to about 20 mole percent benzocyclobutene monomer and about99.99 to 80 mole percent monoalkenyl arene monomer.
 6. The AB blockcopolymer of claim 1 containing randomly distributed pendantbenzocyclobutene structures in the A block.
 7. The ABA block copolymerof claim 1 containing randomly distributed pendant benzocyclobutenestructures in the A blocks.
 8. The (AB)_(m) Y block copolymer of claim 1containing randomly distributed pendant benzocyclobutene structures inthe A block.
 9. A process for preparing an AB block copolymercomprising:(a) solution polymerizing a monoalkenyl arene monomer and abenzocyclobutene monomer of the formula ##STR9## where R is H or CH₃under polymerization conditions at a temperature between about -75° C.and +150° C. with a organomonolithium initiator therein forming a livingpolymeric arm A-Li; (b) contacting said living polymeric arm A-Li with aconjugated diene monomer therein forming a polymeric arm AB-Li; and (c)recovering the resulting block copolymer AB.
 10. A process for preparingan ABA block copolymer comprising:(a) solution polymerizing amonoalkenyl arene monomer and a benzocyclobutene monomer of the formula##STR10## where R is H or CH₃ under polymerization conditions at atemperature between about -75° C. and +150° C. with an organomonolithiuminitiator therein forming a living polymeric arm A-Li; (b) contactingsaid living polymeric arm A-Li with a conjugated diene monomer thereinforming a polymeric arm AB-Li; and (c) contacting said living polymericarm AB-Li with additional monoalkenyl arene monomer and benzocyclobutenemonomer, therein forming a polymeric arm ABALi; and (d) recovering theresulting block copolymer ABA.
 11. A process for preparing a blockcopolymer (AB)_(m) Y comprising:(a) solution polymerizing a monoalkenylarene monomer and a benzocyclobutene monomer of the formula ##STR11##where R is H or CH₃ under polymerization conditions at a temperaturebetween about -75° C. and +150° C. with an organomonolithium initiatortherein forming a living polymeric arm A-Li; (b) contacting said livingpolymeric arm A-Li with a conjugated diene monomer therein forming apolymeric arm AB-Li; and (c) contacting said living polymeric arm AB-Liwith a coupling agent therein forming the block copolymer (AB)_(m) Ywhere Y is the residue of the coupling agent and "m" is between 1 and30.
 12. The process of claim 9 wherein said monoalkenyl arene monomer isstyrene and said conjugated diene is selected from the group consistingof butadiene and isoprene.
 13. The process of claim 9 wherein saidbenzocyclobutene monomer is 4-vinylbenzocyclobutene.
 14. The process ofclaim 10 wherein said monoalkenyl arene monomer is styrene and saidconjugated diene is selected from the group consisting of butadiene andisoprene.
 15. The process of claim 10 wherein said benzocyclobutenemonomer is 4-vinylbenzocyclobutene.
 16. The process of claim 11 whereinsaid monoalkenyl arene monomer is styrene and said conjugated diene isselected from the group consisting of butadiene and isoprene.
 17. Theprocess of claim 11 wherein said benzocyclobutene monomer is4-vinylbenzocyclobutene.
 18. The process of claim 12 wherein saidmonoalkenyl arene monomer is styrene and said conjugated diene isselected from the group consisting of butadiene and isoprene.
 19. Theprocess of claim 12 wherein said benzocyclobutene monomer is4-vinylbenzocyclobutene.